1. Field of the Invention
The present invention relates to a non-aqueous secondary lithium battery with a negative electrode comprising metal lithium, a lithium alloy, or a host compound which forms an intercalation compound or complex with lithium ions.
2. Discussion of Background
A secondary lithium battery is expected to be put to practical use, not only as a power source for portable electronic appliances, but also as a power source for electric automobiles and as a power source for power storage.
However, conventional secondary lithium batteries using metal lithium as a negative electrode thereof have problems in the cycle life and safety thereof when used in practice, so that a secondary lithium battery with satisfactory performance has not yet been developed. It is considered that this is partly because a negative electrode with satisfactory performance for the secondary lithium battery has not yet been developed.
One problem of the negative electrode of such conventional secondary lithium batteries, when used in practice, is that the metal lithium used in the negative electrode is so reactive that the surface of the negative electrode is apt to react with a solvent in contact therewith.
Lithium ion is reduced during the charging of the battery, so that metal lithium is formed. However, the metal lithium is apt to be formed in the form of dendrite, which has a problem of destroying an insulating separator disposed between a positive electrode and the negative electrode.
In order to solve this problem, additives for an electrolytic solutions have been studied as reported in "Denka" 57, 523 (1989) by M. Morita, S. Aoki and Y. Matsuda; and Progress in Batteries & Solar Cells, Vol. 8 (1989).
Furthermore, new negative electrodes using as a negative electrode material therefor an intercalation compound in which lithium ions are incorporated, a carbon material in which metal lithium is stabilized, or a ceramic material, are now being developed.
Examples of an intercalant for lithium ion are natural graphite, pyrolytic carbon prepared by thermal decomposition of coal, coke or organic materials; and carbon materials obtained by carbonizing natural polymers and synthetic polymers. Such carbon materials may be in various forms such as in the forms of porous powder, carbon fibers, and glassy carbon.
Varieties of active carbon materials for the negative electrode have been proposed.
For example, a conducting carbon material obtained by carbonizing furfuryl resin at 1100.degree. C. is proposed in Japanese Laid-Open Patent Application 2-66856; a conducting carbon material which is obtained by thermal treatment of an aromatic polyimide in the atmosphere of an inert gas at 2000.degree. C. or more is proposed in Japanese Laid-Open Patent Application 61-277165; and a graphite prepared from graphite-like spherical carbon particles is proposed in Japanese Laid-Open Patent Application 4-115457.
Japanese Laid-Open Patent Application 61-77275 discloses a secondary battery comprising an electrode which is made of an insulating or semiconductive carbon material with a polyacene structure, which is prepared by subjecting a phenolic polymer to heat treatment.
Secondary batteries by use of the above negative electrodes are of an ionic system type and are in fact improved with respect to the cycle life and battery performance. However, the current characteristics thereof are insufficient for use in practice.